Define dangerous.... HPV has been around since before we knew all the problems it was associated with. In the pre vaccine era as many as 70% of young adult females tested positive for exposure & some studies suggest even more. Most live their life & never have any negative outcome. Some strains produce cancer in fraction of those infected but it may not show up for decades. There are more serious and aggressive STD's.
Risk of cancer. Young or old, infection with hpv is a risk factor in the causation of cervical, oral, and anal cancer. Vaccination can prevent infection with the common strains causing cancer.